1. Field of the Invention
This invention relates to an assembly jig for manufacturing a long structure with an arcuate cross section such as a roof construction of railway carriages etc., and more specifically to an adjustable jig with curved surfaces.
2. Description of the Related Art
A long structure like a roof construction of a railway carriage is generally constructed from a roof board, cross members, and longitudinal members, and has generally an arcuate cross section. The conventional methods for manufacturing such a construction require therefore the use of an assembly jig comprising a curved jig with an arcuate cross section. For example, the roof construction of the railway carriage is made by the steps of placing, on the concave surface of the jig, thin steel sheets in parallel side by side, welding them to each other, laying down a roof framing of the steel sheets, and welding or tack welding the roof framing to the steel sheets.
The manufacture of various roof constructions with arcuate cross sections of various radii of curvature requires various special assembly jigs for different roof constructions. Therefore, the assembly jigs have to be replaced for different one before conducting another assembling of different roof constructions.
The conventional curved jigs thus suffer from the following disadvantages:
(a) The curved jigs have to be replaced for another one for a different roof construction with a different cross section. PA1 (b) Since the curved jigs used in this kind of work are very heavy, an overhead travelling crane or a fork-lift truck has to be used to move them in the replacement operation. PA1 (c) Since the curved jigs are made of thick steel plates, it is difficult and time-consuming to shape the thick steel plates to the curvature required. PA1 (d) During welding of steel sheets on the curved jig to form a roof board, the heat of the welding might cause distortion in the shape of the curved jigs, with a resultant loss of precision of the curved jig. PA1 (e) Where various curved jigs with different curvatures are prepared in advance, they require a wide storage space. On the other hand, where the curved jig is made up specially at each time, it takes up a great deal of time. PA1 (f) Since the curved jigs are made up from a plurality of steel plates welded to each other end to end, the longitudinal alignment is poor, which in turn means the overall shape of the finished roof construction is not good. PA1 (g) An exchange of the curved jigs requires much time and hard labor. PA1 (a) Work required to alter the curvature of the adjustable curved jig to fit new specifications can easily be done by a single operator in the minimum time. PA1 (b) The invention completely eliminates the need for the preparatory work which, in the conventional art, is required in replacing the assembly jig for another one. PA1 (c) The adjustable jig can be adjusted to the desired curvature simply by selecting the appropriate step of the pedestal, or by replacing the pedestal for another one. PA1 (d) There is no need to use a crane or a fork-lift truck in changing the curvature of the curved jigs. PA1 (e) Complete safety is assured in changing the curvature of the curved jig, since no heavy objects have to be moved. PA1 (f) Unbroken rails are used for defining the long jigs, as distinct from the joined sheets in the conventional art, resulting in greater precision of the longitudinal alignment and in improved quality of the finished products. PA1 (g) The heat of the welding less affects the curved jig, since the separate rails are used as distinct from the conventional art using an integral welded surface plate. Thus, the precision of the curved jig is maintained and the quality of the product is improved.